While there is no evidence of harm to patients from exposure to anesthetic gases such as nitrous oxide, some studies suggest that such gases may be detrimental to the health of dental personnel who are exposed to them. Thus, for example, dental personnel exposed to anesthetic gas have been found to have significantly more kidney and liver disease than those who are not so exposed. Further, the incidence of spontaneous miscarriages with female dental workers exposed to anesthetic gas has been found to be higher than in the case of those not so exposed.
Efforts have been made in the past to design systems for administering an anesthetic gas which prevent the escape of gas to the atmosphere where it can be inhaled by dental personnel. Thus, there is disclosed in U.S. Pat. No. 4,015,598, the disclosure of which is incorporated herein by reference, a nasal mask having a second outer wall to form an exhaust passage communicating with the inner portion of the mask and having an open lower peripheral edge for scavenging gas leaking from the mask, the said exhaust passage being connected to a source of vacuum. Such prior art masks in systems for administering anesthetic gas involve a number of problems. Patient breathing is not always well adjusted to the capacity of the vacuum system. If the patient breathes out more than the vacuum system can handle, the patient blows the mask away from his face and nose permitting anesthetic gas to be discharged into the atmosphere. On the other hand, if the vacuum capacity is too great, it draws from the breathing bag wasting anesthetic gas. Further, the prior art face masks do not fit closely on many patients resulting in the unwanted escape of anesthetic gas and tending to cause unwanted marking of the patient's skin since they tend to be strapped on very tightly to prevent the unwanted escape of anesthetic gas.
Another prior art technique is to cover the patient's head including the nasal mask with a hood having a negative pressure within the hood. However, the hood is inconvenient for dental personnel and is objectionable to the patient when awake.
The problems of blowing the mask off the face and unnecessarily withdrawing anesthetic gas from the breathing bag have been solved by this invention by providing a reservoir in the vacuum system. In addition, the invention provides scavenging nozzles for the face mask which are connected to the vacuum system by lines separate from the lines accommodating the patient's exhalation thus preventing exhalation to the atmosphere through the scavenging system as is possible with the prior art mask first described above. Further, the invention provides a mask which can be adjusted so as to fit the particular patient to which it is to be applied.